Electron discharge devices



April 2, 1963 D. H. WHITE 3,084,278

ELEcTRoN DISCHARGE DEVICES Filed Deo. 18, 1959 l? I, v5I 22 VWM? d' 26 E .1 @B d3 AUM25 /N VEA/70H DA \//D H. WH/ TE MMM A Trop/wwv United States Patent O ware Filed Dec. 18, 1959, Ser. No. 860,593 9 Claims. (Cl. 31E-39.3)

The present invention relates to electron discharge devices having crossed electric and magnetic fields, and more particularly to a new and improved electron gun collector for use in such devices.

An electron discharge device having crossed electric and magnetic fields, whether linear or circular, comprises essentially an electron gun including a cathode and an accelerating anode `spaced from the cathode and maintained at a positive potential with respect thereto. Adjacent the electron gun is the main or active part of the tube which may comprise a periodic delay line anode Vor the like and a negative electrode or sole arranged oppositely from but adjacent to the anode. The electron beam produced by the electron gun is caused to traverse the interaction space between the periodic delay line and sole under the combined iniiuence of a radial or normal electric field established between the periodic structure and the sole and a magnetic field transverse to the electric field and electron beam. At the end of the anode opposite from the electron gun is disposed a collector electrode perpendicular to the direction of electron travel to collect the electrons in the electron beam which lalso `functions to render the beam non-reentrant in the case of a circular type tube. So far as is known, once a generally rectilinear beam is produced it is not thereafter modified to improve the electron collection yefiiciency, i.e. the standard crossed field electron gun utilizes the cycloidal trajectories of electrons in crossed D.C. electric and magnetic lields to obtain a rectilinear beam in the interaction space.

This prior art structure is based on the knowledge that electrons which are subjected to mutually perpendicular, or crossed, electric and magnetic lields are caused to .traverse a trochoidal path with a r-ate of progression along the axis of the trochoid determined by the strength of the iields and the initial velocity of the electrons. However, for instance, if an electron is injected into mutually perpendicular electric and magnetic fields of which the electric field has a value of ten volts per centimeter and the magnetic `ield has a value of 1,000 gauss, the electron will progress in the Z direction which is at right angles to both iields, that is to say, in the direction of the axis of the cycloid, at an average speed of one centimeter per microsecond.

The general object of the present invention is to reverse in a tube `of the type referred to hereinabove the operation of the standard crossed field electron gun at the collector electrode and to improve the operating eficiency of such tubes.

-ln an experimental M type back 'wave oscillator tube incorporating the invention a maximum collector efciency of 95 percent was attained. Even for an uncooled collector and somewhat higher currents a high collector etliciency of 75 percent was still obtained.

It is, therefore, an object of the present invention to provide an improved electron gun `structure in a crossed iield tube.

Another object of the present invention is to provide a. crossed field tube having a high collector efficiency that may be simply and economically produced.

With these and other objects in view, the invention may be defined as including an electron gun for electron discharge tubes having crossed electric and magnetic 3,084,278 Patented Apr. 2, 1963 ice fields and a depressed collector coextensive with and on approximately the same radius as, but electrically separated from the sole and an auxiliary electrode oppositely disposed from the collector electrode to cause the electron beam at the end of the interaction circuit to complete the cycloidal arch started at the gun region and to arrive at the collector with reduced velocity.

The foregoing and other objects and -features of the present invention will appear more fully hereinafter yfrom the detailed description which follows taken together with the accompanying drawing wherein specilic embodiments of the invention are illustrated `by way of example. It is to be understood, however, that the drawing is tor the purpose of illustration and Idescription only and [is not intended as a definition of the limits of the invenlOIl.

1n the drawing:

FIG. 1 is a diagrammatic representation partly in .cross isection of a linear device in accordance with the invention; and

FlG. 2 is a diagrammatic representation of a circular device in accordance with the invention.

The principles underlying the invention are conveniently explained with reference to FIG. 1 wherein are represented diagrammatically a conventional housing 11 containing therein a thermionic emissive cathode 12, a heater 13, a battery 14 for supplying a current to the heater 13 to heat the cathode 12, an accelerating electrode 15 at a potential El supplied by battery 16, an anode 17 comprising a delay line at a potental E3 supplied by battery 18, a sole 19 maintained at a potential negative with respect to the anode 17 by battery 21, an auxiliary electrode 22 maintained at a potential equal to or greater than E1 such as, for example, by battery 23, and a collector electrode 24 located on approximately the saine radius as the cathode 12 and maintained at a potential equal to or positive with respect to the cathode 12 and the sole 19 by battery 25. In addition to the electric field established between the accelerating anode 15 and cathode 12 of the electron gun, a magnetic ield l normal to the electric field is produced and is indicated 1n the drawing by the circles containing a cross. It is assumed for the purpose of explanation that the uniformity of the iields E and B is not materially disturbed by any edge effects or by thepresence of the cathode 12 or the collector `24. Assuming further that the electrons are released at Zero velocity at the cathode 12, according to known principles, the electrons will travel in a trajectory such as that shown in the curve 26, which is a common cycloidal arch. The assumed conditions may readily be approximated in practice. In the gun region of the tube shown diagrammatically in FIG. 1, the

trajectory of an electron leaving the center of the cathode 12 is given by:

where d1 is the cathode-accelerating electrode distance,

is the DC. electric iield in the Y direction, B is the D.C. magnetic induction normal to the plane of the trajectory wc is the cyclotron frequency, and t is time. When the Y coordinate of the eletcron path reaches its first maximum, the electron enters the interaction space where the magnitude of the electric potential times the electronic charge is equal to the kinetic energy of the electron.

Astantially concentric wi-th the anode structure.

3 Under these conditions, the electron will travel in the Z direction with a velocity Ve given by Erl-IEA Bdz and with no motion in the Y direction. lt, at the end of the active region, the electron nds itself in aV Y directed D.C. electric field Y it will complete4 the cycloidal arch started in the gun'region, and arrive at the collector electrode .24,` the collectorysurface of which is located on approximately the same radius as the emiting surface of the cathode i2. `The auxiliary electrode-collector distance d3 may be ap- `proximately equal to the cathode-accelerating electrode distance d1.v

j AIn order to-achieve the above-mentioned result it is necessary to introduce the insulated auxiliary electrode 22 to produce the required DC. electric iield in the `collector region, and to match the equipotentialsin the collector regionto those in the interaction or active space region. Since, in an operating tube, the average position of the beammoves toward the anode i7 in the interaction or active space region, the collector electrode 24 and auxiliary electrode 2,2 ideally should be at some higher voltage to circular traveling wave tubes, as shown in FIG. 2.

For purposes of clarity the various connections to the tube-'electrodes have been omitted. rthe tube of FIG. 2;,includes an arcuate periodic anode structure 31 spaced from a concentrically disposed sole or principal electrode 32,10 form the usual interaction space 33. As shown in FIG. Zthe periodic anode structure 31 is of the interdigital type including a plurality of interdigital fingers 341spaced from a circumferential hack wall 35. The invention, however, is not limited to interdigital periodic kstr-,uotures. For example, theanode may be a periodically loaded waveguide or strapped vane structure.

The cathode 36 is mounted Within an elongated slot 37 inthe sole. An-accelerating4 electrode 38 is arranged opposite the cathode 36. The electron beam after traversing-a one-half cycloidal orbit 39, is projected through the interaction space 33 along an arcuate path 41 sub- The insulated auxiliary electrode 42 and lead .thereto is mounted in an elongated slot 43 in the circumference Vback wall and the collector 44 is mounted in an elongatedslot y45 in the sole opposite slot 43 Vand auxiliary electrode 42. This structure results in a non-reentrant tube. The previously required collector structure for a nonreentrant beam tube that formed a part of and extended from the back to a point adjacent the sole is not necessarytandisconsequently omitted. Although not shown in FIG. 2, for reasons of clarity, a radial electric field is established between the periodic anode structure 31 and the sole 32 while a transverse magnetic iield is es- `tablished normal thereto, and in the plane of the paper. One of thefpole pieces 46 of the magnetic field-producing means is/shown inFIG. 2. Y

The present invention is not limited Vto the particu- 'lar details of construction, materials, and processes described, as many ,equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the :appended claims be given a broad interpretation cornmensurate with the scope of the art.

What is claimed is: g

l. In a crossed-held traveling wave device having an elongated interaction circuit the combination comprising: an electron-emitting cathode; a collector electrode; said interaction circuit being located intermediate said cathode and said collector electrode and said cathode and said collector electrode being oriented substantially parallel to extensions of said interaction circuit and energized to produce a given ratio of strengths of said crossed elds; for causing electrons emitted by said cathode to ,travel towardrand thereafter through said interaction circuit; and means, including an auxiliary electrode adjacent the collector end of said interaction circuit oppositely disposed from said collector electrode and en- 2. ln a crossed-field traveling wave device having an .elongate interaction circuit the combination comprising: an electron-emitting cathode; a collector electrode; said interaction circuit being located intermediate said cathode and said collector electrode and said cathode and said collector electrode being oriented substantially parallel to `extensions of said interaction circuit and energized to produce a given ratio of strengths of said Ycrossed fields; for causing electrons emitted by said cathode to travel a cycloidal arch from said cathode to said interaction circuit,V through said interaction circuit and leave said interaction circuit in a direction substantially parallel to said collector electrode; and means, including an auxiliary electrode adjacent the collector end of said interaction circuit oppositely Vdisposed from said collector electrode and energized to produce a different ratio of strengths of said Vcrossed elds, whereby the said electrons-Will complete the cycloidal arch started at the cathode and arrive at the collector electrode with reduced kinetic energy.

3. In a crossed-field traveling wave device having an elongated interaction circuit the combination comprising: an electron-emitting cathode; a collector electrode; said ninteraction circuit being located intermediate said cathode and said collector electrode and said cathode and said collector electrode being oriented substantially parallel to extensions of said interaction circuit and energizedrto produce a given ratio of strengths of said crossed elds, said interaction circuit comprising an anode and a sole oppositely disposed from and negative with respect to said anode; for causing electrons emitted'by said cathode to travel a cycloidal arch from said cathode to said interaction circuit, through said interaction circuit and leave Vsaid interaction circuit in a direction substantially parallel to said collector electrode; and means, including an auxiliary electrode at a potential less than that of said anode adjacent the collectorend of said interaction cir- -cuit oppositely disposed from said collector electrode,

for providing a different ratio of strengths of said crossed fields atV the collector end of said interaction circuit whereby the said electrons will complete -the cycloidal arch started at the cathode and arrive at the-collector electrode with Vreduced kinetic energy.

4. In a crossed-held traveling Wave device having Aa circular interaction' space the combination comprising:

action circuit, through said interaction circuit and leave said Vinteraction circuit in a direction substantially parallel to said collector electrode; and means, including an auxiliary electrode at a potential less than that of said anode adjacent the collector end of said interaction circuit oppositely disposed from said collector electrode, for providing a different ratio of strengths of said crossed fields at the collector end of said interaction circuit whereby the said electrons will complete the cycloidal arch started at the cathode and arrive at the collector electrode with reduced kinetic energy.

5. In a traveling wave electron discharge device including a cathode space bounded in part by a cathode, an interaction space and an electron collecting space bounded in part by an electron collecting electrode; means producing magnetic fields B in said spaces directed transverse to the general motion of electrons in said spaces and means producing electric fields E in said spaces directed transverse to said magnetic ield, the ratio E/B in said interaction space being substantially greater than the ratio E/B in said cathode and said electron collecting spaces and means energizing said cathode and collecting electrode at the same potential.

6. A crossed-field traveling wave device having a slow Wave propagating structure and elongated electrode bounding an interaction space comprising a cathode emitting electrons at a given energy level at the end of said space, an electron collecting electrode at the other end of said circuit space at the same potential as said cathode, means producing transverse electric and magnetic fields of given ratio of strengths in said interaction space for compelling electrons to travel therethrough, an auxiliary electrode disposed opposite said collector electrode and energized to produce a different ratio of strengths of said crossed ields therebetween whereby electrons leaving said space are compelled by said crossed fields to strike said collector electrode at said given energy level.

7. In a traveling Wave device having an elongated interaction circuit with an electron emitting cathode at one end and an electron collecting electrode at the other end of said circuit, means for compelling emitted electrons to travel in energy exchanging relation with waves propagating in said circuit and strike said collecting electrode at substantially the same energy level as electrons leaving said cathode comprising means energizing said cathode and collector at the same potential, means producing first transverse electric and magnetic fields in said interaction circuit for compelling electrons to travel therethrough and means producing second transverse electric and magnetic fields at the collector end of said circuit for compelling electrons leaving said circuit to strike said collector electrode at said same energy level the ratio of strengths of said first fields being dilerent from the ratio of strengths of said second fields.

8. In a traveling wave device having a slow wave propagating structure and elongated electrode forming an interaction space, an electron emitting cathode at one end of said space and an electron collecting electrode at the other end of said space, means for compelling emitted electrons to travel through said space in energy exchanging relation with Waves propagating in said structure and strike said collecting electrode at substantially the same energy level as electrons leaving said cathode comprising means producing first transverse electric and magnetic fields in said interaction space and means producing second and third transverse electric and magnetic fields at the cathode and collector electrode ends of said space, respectively, whereby electrons leaving said cathode travel over part of a cycloidal path and enter said space and electrons leaving said space complete said cycloidal path and strike said collector electrode at said same energy level the ratio of strengths of said first fields being different from the ratio of strengths of said second elds and said third fields.

9. In a crossed-field traveling wave device having an elongated interaction circuit, an electron emitting cathode at one end of said circuit, an electron collecting electrode at the other end of said circuit, means for compelling emitted electrons to travel in energy exchanging relation with waves propagating in said circuit and strike said collecting electrode at substantially the same energy level as electrons leaving said cathode comprising means energizing said cathode and collector electrode at the same potential, means producing first crossed electric and magnetic fields in said space and means producing different crossed electric and magnetic fields at the ends of said space the ratio of strengths of said irst elds being different from the ratio of strengths of said second fields.

References Cited in the le of this patent UNITED STATES PATENTS 2,633,505 Lerbs Mar. 3l, 1953 2,730,648 Lerbs Jan. 10, 1956 2,774,913 Charles Dec. 18, 1956 2,888,610 Dench May 26, 1959 3,003,119 Favre Oct. 3, 1961 

1. IN A CROSSED-FIELD TRAVELING WAVE DEVICE HAVING AN ELONGATED INTERACTION CIRCUIT THE COMBINATION COMPRISING: AN ELECTRON-EMITTING CATHODE; A COLLECTOR ELECTRODE; SAID INTERACTION CIRCUIT BEING LOCATED INTERMEDIATE SAID CATHODE AND SAID COLLECTOR ELECTRODE AND SAID CATHODE AND SAID COLLECTOR ELECTRODE BEING ORIENTED SUBSTANTIALLY PARALLEL TO EXTENSIONS OF SAID INTERACTION CIRCUIT AND ENERGIZED TO PRODUCE A GIVEN RATIO OF STRENGTHS OF SAID CROSSED FIELDS; FOR CAUSING ELECTRONS EMITTED BY SAID CATHODE TO 